I have two;

1.) A coin is tossed four times, and the sequence of heads to tails is recorded.

a) List the sequences in the sample space (I am getting 16...is that right?)

Mr F says: Yes.
b) A=(at least 3 heads); B=(at most two heads); C=(heads on the third toss); D=(1 head and 3 tails)

Find: p(A), p(A intersection B), p(A intersection C), p(A union C), p(B), p(C), p(D)

I just don't understand the intersections & unions. Please explain?

Mr F says: Apply the definitions and use the sample space.
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2.) If p(A)=0.4, p(B)=0.5, and p(A union B)=0.7, find:

a)P(A intersection B) [[I got 0.2]]

Mr F says: Correct.
b) p(A' union B') [Where A' = A complimentary. Please explain, I am lost!]

Thanks so much.